You can protect paginated images against content modifications if your lock level is greater than 0, if the images you are trying to lock are not already protected, and if the page layer you are working on is not protected.
To protect one or more images of an article, select them, and then on the Layout menu, select Lock Content.
Note
The protected images cannot be replaced by Back4- if you drop the same image again in the Back4, it won't be replaced.